Technical Abstract:
Endophyte-infected (Neotyphodium coenophialum) tall fescue (Lolium arundinaceum) produces alkaloids that have been associated with peripheral vasoconstriction in grazing animals and ingestion of these alkaloids may effect splanchnic vasculature. Because of significant differences in morphological and functional characteristics between vasculature supporting digestive and peripheral tissues, the implementation of a bovine foregut vascular model required validation. Experiments were conducted, using dose-responses to norepinephrine (NE) and serotonin (5HT), to evaluate the responses of vessels equilibrated at different tensions and determination of a reference compound. Segments of a branch of right ruminal artery and vein were collected from the ventral coronary groove of healthy mixed breed and gender cattle (n=7) at local abattoirs. Tissues were placed in Krebs-Henseleit buffer and kept on ice until they were trimmed of excess fat and connective tissue, sliced into 2-3 mm sections and suspended on luminal supports in a chamber of a multi-myograph containing continuously oxygenated Krebs-Henseleit buffer (95% O2/5% CO2; pH=7.4; 37°C). Vessels were allowed to equilibrate at either 0.5 or 1.0 g of tension for 1.5 h prior to additions of either NE or 5HT. Increasing doses of each compound were administered in 15-min intervals following buffer replacement. Data were normalized as a percent of contractile response induced by the maximal dose (1×10-4 M) of NE or 5HT for each tension. Ruminal artery and vein both contracted in a dose-dependent manner (P<0.05) to both NE and 5HT treatments. Tension did not affect contractile response of the vein, but 0.5 g tension resulted in a greater arterial response (P<0.05) than 1.0 g. Contractile response to NE was greater than 5HT for both the artery and the vein (P<0.05). These results enable future experiments to separate the effects tall fescue alkaloids have on both the right ruminal artery and vein as representative vessels that support tissues functioning in nutrient absorption.